Potentiometer terminations

ABSTRACT

A potentiometer of the wirewound type having a wirewound helical resistance element with electrical ends precisely positioned at respective locations and wire terminal members economically and accurately fusion-united with the element at said electrical end locations by a procedure including reducing the cross-section of portions of the wire terminals, disposing such portions at respective ones of said locations with the portions on opposite sides of a line parallel to the axis of the helix of the winding and the edges along the line and in line of contact with the wire of the element, fusing fusible electrically conductive material to the wire terminals at said locations, disposing electrical-end portions of the resistance element in contact with the fusible material at respective ones of said locations, and passing heating electrical current through the portions of reduced crosssection of said wire terminal members to fuse said fusible electrically conductive material to said element to fusion-unite and electrically connect said wire terminal members to respective electrical ends of the resistance element. The terminal wire members are embedded in part in a potentiometer body member and exposed at said locations and have terminal end portions extending from the potentiometer body member, and are thus precisely located and maintained in exactly the desired position for welding.

United States Patent [191 Frey, Jr. et al.

[111 3,906,428 51 Sept. 16, 1975 1 POTENTIOMETER TERMINATIONS [75] Inventors: Sydney W. Frey, Jr., Upland;

Robert W. Gaines, Mira Loma, both of Calif.

[73] Assignee: Bourns, Inc., Riverside, Calif.

[22] Filed: July 30, 1974 [21] Appl. No.: 493,193

Related US. Application Data [60] Continuation of Ser. No 340,998, March 14, 1973, abandoned, which is a division of Ser. No. 192,118, Oct. 26, 1971, Pat. No. 3,733,695.

[52] U.S. Cl 338/143; 338/329 [51] Int. Cl. H01C l/144; HOlC 10/24 [58] Field of Search 338/118, 143, 144, 145,

Primary Examiner-Laramie E. Askin Attorney, Agent, or FirmWilliam G. Berker; Richard S. Koppel 57 ABSTRACT A potentiometer of the wirewound type having a wirewound helical resistance element with electrical ends precisely positioned at respective locations and wire terminal members economically and accurately fusion-united with the element at said electrical end 10- cations by a procedure including reducing the crosssection of portions of the wire tenninals, disposing such portions at respective ones of said locations with the portions on opposite sides of a line parallel to the axis of the helix of the winding and the edges along the line and in line of contact with the wire of the element, fusing fusible electrically conductive material to the wire terminals at said locations, disposing electrical-end portions of the resistance element in contact with the fusible material at respective ones of said 10- cations, and passing heating electrical current through the portions of reduced cross-section of said wire terminal members to fuse said fusible electrically conductive material to said element to fusion-unite 'and electrically connect said wire terminal members to respective electrical ends of the resistance element. The

terminal wire members are embedded in part in a potentiometer body member and exposed at said locations and have terminal end portions extending from the potentiometer body member, and are thus precisely located and maintained in exactly the desired position for welding.

5 Claims, 13 Drawing Figures PATENTEDSEP 1's ms 3. 9 O 6.d28

SHEET 1 BF 2 PATENTEUSEP 1 6 ms 3; 906.428 sum 2 OF 2 POTENTIOMETER TERMINATIONS CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation of application Ser. No. 340,998, filed Mar. I4, 1973, now abandoned, which in turn is a division of application Ser. No. 192,118, filed Oct. 26, l97l, now US. Pat. No. 3,733,695.

In respect of certain details this disclosure is related to the disclosure comprised in an application of Sydney W. Frey, Jr., Donald L. Gaa, and Robert W. Tetamore, entitled Precision Potentiometer with Indicator, and Method, Ser. No. 192,119, filed Oct. 26, 1971, now US. Pat. No. 3,723,937.

SUMMARY or THE INVENTION The present invention permits very accurate location of welded connections of molded-in terminals to the resistance-wire of a helical wirewound resistance element in a rotary potentiometer; for example a multiturn potentiometer. As is well understood in the precision potentiometer industry, it is extremely desirable that the connections to the electrical ends of the resistance element be accurately located. For example, it is essential in many applications of ten-turn potentiometers that the electrical ends of the element be exactly 360() rotational degrees apart, whereby each revolution of the contact-actuating shaft from an initial zero position with the contact at one electrical end of the element results in traverse of the contact along exactly a 360 section of the convolution or convolutions of the element until at the end of the final revolution of the shaft the contact reposes exactly in contact with the other electrical end of the element. The same is true whether the potentiometer resistance element comprises a single turn or convolution, or two convolutions, or five or ten convolutions.

Very accurate placement or locating of the electrical connection of the terminals to the electrical ends of the resistance element by first, shaping first and second ter minal members so that a specific edge of a surface of each can be positioned along a line parallel to the axis of the helix of the element and with the surfaces in position for effecting a fusion union of the element and terminal member over the surface, and so conditioning each of the terminal members at the section comprising the noted surface, that effecting the fusion union is facilitated; and second, by embedding intermediate portions of the terminal members in a molded stationary component of the potentiometer while positioned and securely held against movement.

The present invention further provides a structural and electrical arrangement that grossly reduces the time required for effecting fusion-uniting of the terminals with the element, and eliminates necessity for any manual manipulation of any such means as soldering tips and brazing torches. Thus the two element terminals are deformed to provide in each thereof a portion of reduced cross-section and an edge that cooperates with a part of the mold so that the edge is precisely positioned along the noted line, with the adjacent reduced cross-section portions of the two terminals disposed on respective opposite sides of the line. Thus the two edges define connectionpoints that are exactly a whole number multiple of 360 apart along the element. The

noted deformed portions of the respective terminals are further shaped to provide a reverse-bend or U- shaped bend with a fiat surface adjacent the noted edges. The flat surface may be, and in this preferred embodiment of the invention is, utilized for receiving a small thin pad of material used to facilitate fusionuniting of the terminal and the resistance wire of the element. That material may be, depending upon desired results, a solder, a brazing alloy, or other medium; and it is preferably applied as a small flat piece dropped into place on the noted flat surface and fused onto the terminal surface by pressing the pad firmly against the terminal surface by an electrode, and passing an electric current through the terminal, pad, and electrode, the intensity and duration of the current being such as to fuse the pad to the terminal. The arrangement and dimensions of parts are such that the noted flat surface of the reduced cross section portion of the terminal in each case, whether an alloy or like pad is applied, or not, will be positioned to be later contacted by the wire of the resistance element when the latter is mounted upon the noted stationary component of the potentiometer, and with the noted edges of the two terminals aligned and the two surfaces on opposite sides of the noted line parallel with the axis of the helix of the element.

The stationary member in which the terminals are embedded during molding of the member is, in the illustrated potentiometer embodying the invention, a support member that concurrently serves as a mount for the resistance element and terminals and as a means for supporting the potentiometer on an aperture in the panel, all in a mode or fashion shown and described in the aforementioned co-pending disclosure, to which reference may be made as may be necessary. The noted support member is associated with, and permanently united with, a second support member that serves functional purposes not essential to the present invention. Following embedment of the terminal members in the support member and application of the alloy or like pads, if any are to be used, the helical resistance element is mounted on the support with its physical ends extending beyond, or at least extending across, the flat respective surfaces of the terminals. The element, whether of single-turn, two-turns, five turns, ten turns or other multi-turn construction, is formed with a diameter somewhat less than that of the support surface on which it is to be seated, whereby it resiliently expands when applied onto the support and thereafter grips the support. preferably the support is formed with a shallow helical thread, the groove of which intersects openings in the support in which the flat surfaces of the terminals are exposed. Thus the element maybe turned onto the threaded support and precisely positioned and retained in place for cooperation with the potentiometer contact, with end portions contacting the terminals at respective electrical ends of the element.

Following seating of the resistance element on the support with convolutions of the. resistance wire in contact with the fusion-aiding means on the flat surfaces of the terminals, electric currents are passed throughf 'the respective terminals, of sufficient amperage and duration to cause melting and fusion of the material at the points of contact of the resistance wire with I the flat surfaces of the terminals. Thus the element is fusion-united with the terminals at and across the flat surface, with the aligned edges of the two terminals determining the electrical ends of the element. As will be evident to those skilled in the art, a variety of shapes of terminals may be used, within the scope of the invention, to provide accurately positioned electrical ends of a helical resistance element. For example, in a modified form illustrated in this disclosure, the accurately formed terminals have a reduced cross-section at the base of a U-shaped bend and are pressed into respective complementary holes in a support member, and into contact with the resistance wire of an element or with a brazing alloy pad or the like, and are similarly fusion-united to the wire of the element by passing currentof required heating effect. In an alternative construction the modified form of terminal is molded, that is, embedded in the support members. Each of the terminals of modified form is shaped to provide a reduced cross-section'at a rectangular flat surface presenting a straight edge disposed along a line parallel to the axis of the helix of the element, similar to the previously de scribed principal embodiment; and similarly, the flat surfaces of the two terminals are disposed on opposite sides of the noted line whereby to form or provide electrical ends of the element that are an exact wholenumber multiple of 360 apart. In the modified form of support and terminal, the spatial disposition of the flat surfaces as noted is assured by producing the terminalreceiving holes on' opposite sides of the noted line of alignment of the terminal edges. The modified form of terminal may variously be secured in exact and fixed position; but preferably and as herein disclosed. the fixing is effected by provision of support-engaging tangs or barbs along the legs of the U-shaped bend and by machineinsertion of the terminals in the complementary holes. The noted straight edges of the respective terminals abut against respective aligned walls of the holes that contain a line parallel to the axis of the helix of the resistance element. Following insertion and fusion-union with the wire of the resistance element, a wedge-shaped button or insert is driven home to till the space between the two legs or limbs of the U-bend of the element and to firmly embed the barbs into the material of the support. Also, the modified form of terminals is adapted for use in helical-element potentiometers in which the element is brushed by the contact along a surface or track inside the element, whereas those of the principal embodiment are adapted for use in potentiometers having elements brushed by a contact along a path or track outside the element. The principles of the invention are equally applied in both constructions. In the illustrated modified form of terminal member, the terminal is formed by stamping from strip stock which has a brazing alloy or other fusionaiding material incorporated in one surface of the strip.

The preceding summary of the invention indicates that it is a principal object-of the invention to provide general iniprovements in't'erminating the resistance element of a potentiometcr. Another object of the invention is"toprovide an improved potentiometer terminal.

Another object of the invention is to provide a stronger termination. A still further object is to concurrently provide improvements in location and strength ofresistance-element terminations. An additional object is to reduce the cost of potentiometers. Another object of the'invention is to provide improvements in a pair of terminals and associated means for a helical-element rotary potentiometer. Other objects and advantages of the invention will hereinafter be made evident or set out in the following description in detail of a preferred mode and construction according to the invention and the appended claims, all of which relate to the appended drawings.

DESCRIPTION OF THE DRAWINGS In the drawings, FIG. 1 is a pictorial representation to no particular scale, of a potentiometer of known type having a helical resistance of ten electrically active turns or convolutions, but comprising terminals and utilizing an element-termination mode both according to the invention;

FIG. 2 is an enlarged longitudinal plan view of the potentiometer depicted in FIG. 1, with parts broken away to show internal details;

FIG. 3 is a longitudinal sectional view of a principal support member and associated electrical and mechanical means, showing how terminal members are shaped and disposed for fusion-union with an element;

FIG. 4 is a fragmentary plan view of a portion of a support means shown in FIGS. 2 and 3, showing alignment of edges of terminal members along a common line parallel to the axis of a helical element that is shown with parts removed;

FIGS. 5, 6 and 7 are fragmentary sectional views illustrating details;

FIGS. 8 and 8a are elevation and end views, respectively, of a first shaped terminal member of pin form included in thestructure shown in FIG. 3;

FIGS. 9 and 9a are elevation and end views, respectively, of a second shaped terminal member of pin form included in the structure shown in FIG. 3; and

FIGS. 10 and 11 are fragmentary longitudinal and transverse sectional views, respectively, illustrating a modified terminal member formed of sheet or strip material, and mode using stamping techniques.

DETAILED DESCRIPTION OF THE DRAWINGS In FIG. I a potentiometer of known type, modified to embrace the present invention, is denoted generally by number 20. The potentiometer comprises a central axially extending stationary support structure 28, (FIGS.

2 and 3) including a metal bushing 28b embedded in a principal support 28u.of molded insulation. The forward (left) end of support 28:! is formed as a generally hollow cylinder with a shallow external thread providing a helical groove 28g (FIG. 3). Further, the cylindrical portion is formed with two transverse holes A2 and A3 extending inwardly nearly through the wall thereof, as is indicated in FIGS. 3 and 4. During molding of the support 28 three shaped terminals, T1, T2, and T3 are held firmly in predetermined positions in the mold and become partly embedded in the support. The extent to which a middle portion of each is thus embedded is indicatedin FIG. 3. Terminal T1 comprises an inner ring Tla which similarly is firmly embedded in the support with an outer annular surface exposed Terminal T2 is shaped as indicated in FIGS. 8 and 8a, and is so positioned in the mold that a specially formed U-shaped portion of reduced cross-section at a surface S2 is exposed in hole A2 (FIG. 3). Similarly, terminal T3 is shaped as indicated in FIGS. 9 and 9a, and is so positioned in the mold that a specially formed U-shaped portion of reduced cross-section at'surface S3 is exposed in hole A3. Each of the three terminals is spaced from the others thereof, ;and.hence is insulated there- I from. The rear ends of theterminals extend through that portion of the support 28athat is encircled by the metal bushing 28b, and protrude beyond the support to facilitate making of external electrical connections thereto. As is indicated in FIG. 1, the rear ends of the terminals may be formed into hooks At or adjacent their.forward'ends, terminals T2 and T3 are formed as noted with U-shaped bends, and at the latter are reduced in cross-section and deformed to provide respective flat surfaces S2 and S3 (FIGS. 8, 8a, 9 and 9a), that terminate at one side in respective straight edges E2 and E3 (FIG. 4). The terminals are so held in the mold that as thesupport 28a is produced, the noted edges are aligned with each other and disposed along a line L that is parallel to the axis of the helix definedby the groove 28g. Further, the two noted terminals are so dimensioned and disposed that the flat surfaces S2 and S3 are substantially tangent to the bottom of groove 28g, as'indicated in FIG. 3, and lie on opposite sides of line L, as indicated in FIG. 4. Thus when a helical resistance eler'nent'is turned onto support 28a and seated in groove 28g, as illustrated in FIGS. 2, 4 and 6, the flat surfaces are in close juxtaposition with a plurality of points or wire-turns of the element. Preferably, means such as brazing-alloy or solderinserts are first applied onto surfaces S2 and S3 to facilitate a fusion union of the terminals and resistance element. Such added alloy or metal may be very thin, but as will be evident to those skilled in the art, it will rise to contact the element when heated to a liquid state and thus compensate for dimensional tolerances in assembly. When such fusion-aiding alloy or metal is added, it can be inserted into holes A2 and A3 as small flat pieces or punchings, and there fused to the surfaces S2 and S3 by concurrent application of pressure by an electrode and passage of a surge of electric current through the electrode, alloy insert, and terminal in each case As will be evident to those skilled in the art, direct or hot forged" type of welding of the resistance wire to the terminal is also possible and within the province of the invention. Generally, however, fusion-union of the element and terminal is facilitated by employment of brazing alloy to aid the union.

After the terminals have been fixed in position as parts of the subassembly comprising the support 28a, and otherwise prepared as noted, a helical element 32 (FIGS. 3 and 4) is turned onto the thread-bearing forward end of the support and seated in groove 28g with its first and second ends each extending beyond a respective one of the exposed terminal surfaces S2 and S3. Preferably, and as is indicated in FIG. 4, the helical element is made suficiently long to extend at least three-fourths of one turn or convolution beyond the surfaces S2 and S3, the groove 28g having been formed at least one and one-fourth turn beyond holes A2 and A3. Thus the physical ends of the element, such as end 322 in FIG. 4, are disposed beyond the points on line L at which electrical ends of the elements are to be established.

Establishment of accurately positioned electrical terminations or electrical ends of the resistance element is completed by connecting power conductors to ends of the terminals and passing currents through the reduced cross-sections of sufficient magnitude or intensity and duration to cause heating of the terminals at and adjacent the weld points W2 and W3 to a temperature high enough to cause fusion of the material of the resistance wire and/or terminal at the points of contact therebetween across the flat surfaces S2 and S3. If de sired, as may be the case with certain types of resistance-element wire, flux or other fusion aiding means maybe used on the surfaces to promote the-formation of electrical connections of good physical and electrical characteristics and to produce continuous sharply defined connections along the edges E2 and E3. It will be evident that the noted connections for passing heating current through the terminals may be established at the inner ends T2 and T3, and at the outer rear ends, of the terminals, and that following electrical testing of the subassembly the inner ends may besheared off or left in place. Reduction of cross section of terminals at the base of the U-bends at surfaces S2 and S3 may be varied to suit or be compatible with the materials used and allied factors. In the exemplary embodiment, as shown in enlargedscale in FIGS. 5 and 6, the area of the cross-section at the'center of the base of the U- bend, at the mid-point of the edge E3, is approximately 33 percent of the cross-sectional area of the terminal wire used. The exemplary element 32 is 0.03 1 inch nominal diameter, the pitch of the helix 0.041 inch, and the length of edge E3 approximately 0.050 inch. It is made evident by examination of FIG. 5 that the fusionunion of the terminal T3 to the wire of the element occurs in an area across the width of the reducedsection of the terminal from the point denoted Y to the point denoted X, and ends at the edge of the terminal at the latter point. Thereby the electrical end of the element is defined at point Y.

Following electrical testing and acceptance of the terminals-support-element subassembly, a front auxiliary support member (FIG. 2), the shell 24, indicator means 36 and lens 26 are added, as fully set out in the aforementioned co-pending disclosure, to complete the potentiometer 20. The potentiometer is adapted to be secured to a panel through an aperture in which bushing 28b extends, by means of a nut N and washer W, in a fashion known and disclosed in US Pat. No. Re 25,674.

The invention as applied to a potentiometer having an internally brushed helical resistance element is indicated in FIGS. 10 and 11. Therein an internally threaded support 28a carries a helical element 32 that is brushed by a contact 300 driven by a rotor R mounted on a shaft rotatable in bushing 28b, all in a known mode. The support is formed with axially offset apertures of generally rectangular section which have oppositely facing inner flat walls such as 28w that are aligned in a plane containing the axis of the helix of the element 32'. Terminals T2 and T3 having U-bends with reduced cross-section as indicated and having brazing alloy or the like fused onto or otherwise applied to the exteriors of at least the bases of the U-bends, are forced into the apertures and therein locked by barbs such as Tb (FIG. 11) produced on appropriate sides of the terminals. One edge, E2, of the terminal is in each instance left smooth and straight for abutting against one of the aligned walls 28w,- for defining an electrical end of the element 32. The lower corner of the edge of the terminal contactsthe element along a line L parallel to the helix axis, and fusion-union of the element and terminals occurs over portions of the flat lower sur faces of the terminals at W2 and W3, as indicated in FIG. 11. Following passing ofa heating current through the legs of the U-bends of terminals T2 and T3 to fuse the junctions with the element, plastic wedges, F, are driven into the spaces between the legs, with a sealing cement or heat applied, to prevent ingress of undesirable foreign material and to firmly anchor the two terminals in place. A third terminal, Tl, connects with the contact 300 by conventional means known in the art. In other respects the potentiometer shown in fragmentary form in FIGS. 10 and 11 is conventional. An alternative mode and means of securing the terminals T2 and T3 in place is to embed them in the support by insertmolding as described previously in connection with the principal embodiment.

Having described the invention in detail, we claim: 1. A potentiometer comprising: first and second electrical conductors each comprising first and second end portions and an intermediate shaped termination portion of reduced crossseetional area with one face of said intermediate termination portion adapted for connection to a resistance element; a support member comprising means for supporting a resistance element and comprising a portion embedding and accurately fixing in respective positions said first and second electrical conductors with said one face of each of said shaped termination portions of the latter exposed at respective l0- cations by said support member for direct contact with respective electrical ends of a resistance element; and a helical resistance element on said support member with first and second electrical ends thereof fusionunited with respective ones of said electrical conductors at said locations;

each of the endp'ortions of said first and second conductors being adapted to receive and transmit therebetween a current of sufficient magnitude to fusion-unite said resistance element ends with said electrical conductors by heating of said conductors at said locations.

2. A potentiometer as defined in claim 1, in which each of the shaped termination portions of said conductors presents a flat face and an edge. the flat face defining a region of fusion-union with said helical resistance element and the edge defining a limit of the region of fusion-union. the flat faces of the respective termination portions being disposed on opposite sides of a line parallel with the axis of the helical resistance element and the edges of the two termination portions being aligned with said line, whereby the convolutions of said helical resistance element between said edges are an exact whole-number multiple of 360.

3. A potentiometer as defined in claim 2, wherein said support member presents an internal helical surface and said helical resistance element is mounted on said helical surface.

4. A potentiometer as defined in claim 2, wherein said support member presents an external helical surface and said helical resistance element is mounted on said helical surface.

5. A potentiometer as defined in claim 1, wherein the shape of each shaped termination portion of said conductors includes a substantial bend. 

1. A potentiometer comprising: first and second electrical conductors each comprising first and second end portions and an intermediate shaped termination portion of reduced cross-sectional area with one face of said intermediate termination portion adapted for connection to a resistance element; a support member comprising means for supporting a resistance element and comprising a portion embedding and accurately fixing in respective positions said first and second electrical conductors with said one face of each of said shaped termination portions of the latter exposed at respective locations by said support member for direct contact with respective electrical ends of a resistance element; and a helical resistance element on said support member with first and second electrical ends thereof fusion-united with respective ones of said electrical conductors at said locations; each of the end portions of said first and second conductors being adapted to receive and transmit therebetween a current of sufficient magnitude to fusion-unite said resistance element ends with said electrical conductors by heating of said conductors at said locations.
 2. A potentiometer as defined in claim 1, in which each of the shaped termination portions of said conductors presents a flat face and an edge, the flat face defining a region of fusion-union with said helical resistance element and the edge defining a limit of the region of fusion-union, the flat faces of the respective termination portions being disposed on opposite sides of a line parallel with the axis of the helical resistance element and the edges of the two termination portions being aligned with said line, whereby the convolutions of said helical resistance element between said edges are an exact whole-number multiple of 360* .
 3. A potentiometer as defined in claim 2, wherein said support member presents an internal helical surface and said helical resistance element is mounted on said helical surface.
 4. A potentiometer as defined in claim 2, wherein said support member presents an external helical surface and said helical resistance element is mounted on said helical surface.
 5. A potentiometer as defined in claim 1, wherein the shape of each shaped termination portion of said conductors includes a substantial bend. 